The Network Diagnostic Tool (NDT) provides a sophisticated speed and diagnostic test. An NDT test reports more than just the upload and download speeds — it also attempts to determine what, if any, problems limited these speeds, differentiating between computer configuration and network infrastructure problems. While the diagnostic messages are most useful for expert users, they can also help novice users by allowing them to provide detailed trouble reports to their network administrator.

NDT can make use of either a Java plugin, or WebSockets to perform the test. Make sure that the method you choose is supported by your browser

The WebSocket client currently in beta. Due to the nature of WebSocket support in various web browsers, the results may be notedly lower than those obtained with the Java plugin.